1. Field of the Invention
This invention relates to an apparatus for determining at least one size parameter of an object whether it is moving or at rest, which apparatus comprises an optoelectronic measuring system, which includes light transmitting and receiving elements disposed in at least one measuring plane that is substantially at right angles to the longitudinal axis of the object, and also includes an evaluating unit, wherein the measuring plane is defined by a measuring portal comprising at least two support beams for the light receiving elements of the measuring system, which include a predetermined angle with each other.
2. Background of the Invention
Austrian Patent Specification 351,282 discloses an apparatus for determining and/or monitoring at least one size parameter of an object whether it is moving or at rest, which apparatus comprises line cameras disposed in two planes, which include an angle of 90.degree., which cameras instead of a film comprise a surface provided with rows of photodiodes for generating an electronic image of the shadow of an object which is disposed in front of a bright background and viewed through an optical system.
That apparatus is rather expensive owing to the provision of the line cameras and has the disadvantage that in dependence on the position of the object being viewed the image of its shadow may be unsharp so that the accuracy of the measurement may adversely be affected.
German Patent Publication 2,019,290 and Published German Application 2,127,751 disclose apparatuses in which the object to be measured is periodically scanned so that an overall image of such object can never be generated at any specific instant. Those apparatuses have also the disadvantage that they require light transmitters or mirrors which are mechanically moved.
Other known apparatuses comprise support beams, in each of which a row of infrared-emitting diodes are closely and regularly spaced apart in a row and an infrared photodiode is associated with each of said rows and is disposed in the measuring plane and centered with respect to the support beam. The infrared-emitting diodes are consecutively activated together with the associated infrared photo-diode after short, equal intervals of time by an evaluating unit.
That apparatus for a periodic scanning has the disadvantage that the adjustment of the infrared-emitting diodes takes a long time and can be effected only with expensive means, such as an oscillograph. Besides, the signals generated by the infrared photo-diodes are relatively weak and must be amplified before they can be processed further. But such amplification may result in a drifting or change or the parameter as a function of time and temperature so that the result of the measurement may be distorted.